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The i.MX UART peripheral uses the RST_B signal as input, and CTS_B as
output. This is just like the DCE role in RS-232. This is true
regardless of the "DTE mode" setting of this peripheral.
As a result, rs485 support hardware must use the CTS_B signal to control
the RS-485 transceiver. This is in contrast to generic rs485 kernel
code, documentation, and DT property names that consistently refer to
the RTS as transceiver control signal.
Add a note in the DT binding document about that, to reduce the
confusion somewhat.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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rs485 allows for robust half-duplex serial communication. It is often
implemented by attaching an rs485 transceiver to a UART. The UART's
RTS line is wired to the transceiver's Transmit Enable pin and
determines whether the transceiver is sending or receiving.
Examples for such transceivers are Maxim MAX13451E and TI SN65HVD1781A:
https://datasheets.maximintegrated.com/en/ds/MAX13450E-MAX13451E.pdf
http://www.ti.com/lit/ds/symlink/sn65hvd1781a-q1.pdf
In the devicetree, the transceiver itself is not represented, only the
UART is. A few rs485-specific dt-bindings already exist and these go
into the UART's device node.
This commit adds a binding to set the RTS polarity. Most (if not all)
transceivers require the Transmit Enable pin be driven high for sending,
but in some cases boards may negate the pin and RTS must then be driven
low. Consequently the polarity defaults to active high but can be
inverted with the newly added "rs485-rts-active-low" binding.
Document this binding in rs485.txt and in the two drivers fsl-imx-uart
and fsl-lpuart that are about to be amended with support for it.
Curiously, the omap_serial driver defaults to active low and already
supports an "rs485-rts-active-high" binding to invert the polarity.
This is left unchanged to retain compatibility, but the binding is
herewith documented.
Cc: Mark Jackson <mpfj@newflow.co.uk>
Cc: Michał Oleszczyk <oleszczyk.m@gmail.com>
Cc: Rafael Gago Castano <rgc@hms.se>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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'fsl,irda-mode' property has been removed since commit afe9cbb1a6ad
("serial: imx: drop support for IRDA"), so remove it from the binding
document.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Atmel USART, Freescale UARTs and OMAP UART all support the rs485 binding
described in rs485.txt, this commit just makes that explicit.
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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This reverts commit a3015affdf76ef279fbbb3710a220bab7e9ea04b as there
are complaints that it is incorrect.
Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Nandor Han <nandor.han@ge.com>
Cc: Romain Perier <romain.perier@collabora.com>
Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
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The size of the DMA buffer can affect the delta time between data being
produced and data being consumed. Basically the DMA system will move
data to tty buffer when a) DMA buffer is full b) serial line is idle.
The situation is visible when producer generates data continuously and
there is no possibility for idle line. At this point the DMA buffer is
directly affecting the delta time.
The patch will add the possibility to configure the DMA buffers in DT,
which case by case can be configured separately for every driver
instance. The DT configuration is optional and in case missing the
driver will use the 4096 buffer with 4 periods (as before), therefore no
clients are impacted by this change.
Signed-off-by: Nandor Han <nandor.han@ge.com>
Signed-off-by: Romain Perier <romain.perier@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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'uart-has-rtscts' is a generic serial property and it is described
at Documentation/devicetree/bindings/serial/serial.txt, so remove it
from the specific fsl-imx-uart binding documentation.
While at it, add a note pointing to the serial.txt file, which
contains the complete list of generic serial bindings.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Rob Herring <robh@kernel.org>
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Convert the Freescale IMX UART driver from using the vendor-specific
"fsl,uart-has-rtscts" to the generic "uart-has-rtscts" DT property, as
documented by the Generic Serial DT Bindings.
The old vendor-specific property is still recognized by the driver for
backwards compatibility, but deprecated.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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We should say "The uart works in DCE mode".
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Rob Herring <robh@kernel.org>
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Move all bindings in bindings/tty/serial into bindings/serial so we only
have one place dir with serial/uart related bindings in it.
Signed-off-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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We had two bindings for the same serial device, it looks like the one in
tty/serial/fsl-imx-uart.txt is the more up to date one so go with it and
merge a few things about the use/need for aliases in from
serial/fsl-imx-uart.txt.
Signed-off-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Add documentation for imx serial.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
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